SOLUTION: Laura received an e-mail from Billy. After 10 minutes Laura forwarded it to 3 of her friends. After 10 minutes each of those 3 friends forwarded the message to 3 more friends. If t

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Question 736767: Laura received an e-mail from Billy. After 10 minutes Laura forwarded it to 3 of her friends. After 10 minutes each of those 3 friends forwarded the message to 3 more friends. If the message was forwarded like this every 10 minutes, how many people had received Billy's e-mail after 50 minutes?
Answer by mananth(16946) About Me  (Show Source):
You can put this solution on YOUR website!
Laura received an e-mail from Billy. After 10 minutes Laura forwarded it to 3 of her friends. After 10 minutes each of those 3 friends forwarded the message to 3 more friends. If the message was forwarded like this every 10 minutes, how many people had received Billy's e-mail after 50 minutes?

the email was sent every 10 minutes
Total emails 5
first email 3, 9,27 81, 243.....
it is a GP
Sn=a%28r%5En+-1%29%2F%28r-1%29

Sn+=+3%283%5E5-1%29%2F%283-1%29

Sn = 3*242/2
=363 emails will be sent in 50 minutes